This invention relates to a bead retainer which is capable of maintaining the beads of a tire in contact with the flanges of a rim. More particularly, this invention relates to a tire and rim assembly having a device that enables the beads of a tire to be held against the flanges of a multi-piece rim. Still more particularly, this invention relates to a device for improving the low pressure travel performance of a tire/rim assembly when used with or without a central inflation system. This invention also relates to a fastening means for fastening and unfastening a bead retainer device.
As used herein, the bead retainer, also known as a bead lock and/or a bead spacer is a structure that is used to maintain the beads of a tire in contact with the flanges of a rim. Preferably, the beads of a tire are not only held in contact with the flanges, but also are not generally subject to rotation with respect to the flanges. The bead retainer according to the invention herein, is not to be considered a run-flat insert. For use in this specification, a run-flat insert is considered to be a device for use inside a pneumatic tire to support the weight of the vehicle in the event the tire is deflated. Although the bead retainer device may be used under conditions of low or zero tire pressure to enhance the tire's travel performance, the bead retainer device is not intended to support the weight of the vehicle in such conditions.
A bead retainer device can however improve the run-flat characteristics of a tire to a certain degree by keeping the beads of a tire in place. Without the bead retainer device the beads of the tire would pull away from the rim bead seat and would be quickly damaged by the rim during travel of the vehicle. Therefore, by keeping the bead seated on the rim there is less chance of tire failure in this manner.
Bead locks have also begun to be used with systems known as central tire inflation systems. In a central tire inflation system, air pressure can be either added to or taken from the tire cavity to improve the ground travel characteristics of a tire depending upon the surfaces encountered. For example, reducing the air pressure within a tire when the vehicle is traveling over soft, marshy, or sandy ground will increase the footprint of the tire thereby improving traction and flotation. Therefore, systems have been developed in order to compensate for the different types of surfaces or ground conditions encountered. A tire may be taken from a normal inflation pressure to a very low inflation pressure. As used herein, a very low inflation pressure is one on the order of about 0.7 to 1.0 BAR. The tire can then be inflated back to the normal inflation pressure by pumping air back into the tire cavity. Without a means for retaining the bead portion of the tire against the flanges of the rim, the beads would become unseated at very low inflation pressures thereby causing a complete deflation of the tire which would not allow for its later reinflation.
Bead retainers can also help keep the beads seated when the tire is subjected to off-road conditions. For example construction vehicles and such are subjected to conditions wherein side forces tend to try to pull the beads off the rim and deflate the tire. Bead retainers are also helpful when a tire is subjected to extreme changes in temperature. In that the inflation pressure of a tire varies as a function of temperature, the beads of a tire may become unseated when the ambient temperature becomes very cold, causing the inflation pressure to drop. This can occur especially during rapid temperature changes during the winter and especially in the arctic regions.
Various bead retainers have been tried in order to keep the beads against the rim. For example U.S. Pat. No. 4,558,728 to Forneris proposes the use of an elastomeric material located between the bead portions of a tire and having a reinforcement member contained in the elastic material in order to keep it seated on the rim. Another device that has been used in order to lock the beads to the rim of a tire is taught in U.S. Pat. No. 2,383,577 to Zarth. This device is an annular ring comprising metal that is fastened together by a kinamatic hinge structure. This device is expensive to manufacture in that it requires rolled edges and a complex hinge structure. This device, being comprised of metal is also fairly heavy.
The problem with most if not all prior art devices has been weight. One of the prime concerns of a tire/rim assembly is the total weight of such an assembly. Any additional weight to an assembly has a negative effect on the vehicle as a whole, one such effect being the reduction in fuel economy. The total weight also is reflected in how easily it is to install and remove the assembly.
Another problem that has been associated with bead retainer devices has been the difficulty in which they can be mounted and dismounted within the tire and onto the rim assembly. Some one-piece hoop-like elastomeric members that have been used for bead-lock devices are pre-tensioned such that they have an internal diameter that is equal to or less than the external diameter of the rim, thereby clamping itself to the rim. In that the diameter is equal to or less than the diameter of the rim the device must be stretched and expanded over the rim in order to install it. Other elastomeric devices that have diameters that are equal to the rim generally must be compressed by a machine and then banded together with a tie or other banding material. The banded together bead retainer is then forced between the beads of the tire and once inserted after much prying and force is allowed to return to its original shape by removing the banding material. Another disadvantage of an elastomeric bead retainer device is that they generally are axially compressible, thereby requiring the width of the bead retainer to be from at least 7 to 10% greater than the distance between the beads when mounted on a rim in order to compensate for the device taking a compression set and allowing the bead portions to become unseated. The extra axial width therefore imparts added weight to the device.